This invention relates to a motor control technology.
Conventionally, a control system is known in which disturbance is estimated by a disturbance observer and a control input is corrected based on the estimated disturbance. FIG. 7 is a block diagram of a conventional motor control system 900 using a disturbance observer 910.
The control system shown in FIG. 7 is designed as follows. First, a transfer function G(s) of a controlled object (plant) is derived. Then, on the assumption that a relationship between a control output y and a control input u satisfies y=G(s)·u, a controller 920 is designed to output the control input u corresponding to a target control output yr.
The control input u outputted from the controller 920 is corrected by adding thereto a correction amount d* generated in the disturbance observer 910. Disturbance is suppressed by inputting a corrected control input uc=u+d* into the controlled object, and the control output y is controlled to the target control output yr.
Specifically, the disturbance observer 910 generates a correction signal (uc−1/G(s)·y) for suppressing disturbance based on an inverse model 1/G(s) of the transfer function G(s) and the control input uc. The disturbance observer 910 filters the correction signal through a low-pass filter 930, and outputs a filtered correction signal as a correction signal representing the above correction amount d*.
A reason why the correction signal (uc−1/G(s)·y) is filtered through the low-pass filter 930 is because of frequency characteristics exhibited by the transfer function G(s) of the controlled object and by the inverse model 1/G(s). That is, while the transfer function G(s) exhibits frequency characteristics in which the higher a frequency of an input signal to the transfer function G(s) is, the lower a gain becomes; the inverse model 1/G(s) exhibits frequency characteristics in which the higher a frequency of an input signal to the inverse model 1/G(s) is, the higher the gain becomes.
Accordingly, when a measured control output y is inputted into the inverse model 1/G(s) to generate the correction signal (uc−1/G(s)·y), observation noise included in high-frequency band is amplified in the correction signal. Therefore, the low-pass filter 930 is used to suppress influence of the observation noise and accurately achieve disturbance suppression.
Also, there is a known motor control system using estimated disturbance by a disturbance observer in which a control input to a motor is corrected so as to compensate a motor torque corresponding to the static friction, by considering that it takes substantial time before a motor torque overcomes static friction to displace a driven object.